The invention relates to an electrophotographic apparatus in which the image of an original is projected through an exposure controller onto a light-sensitive member which is previously uniformly charged, to form an electrostatic latent image thereon, and more particularly to such apparatus in which a positive copy image is obtained for either a negative or positive original by using a toner of a fixed polarity as a developer and by switching the polarity with which the light-sensitive member is charged.
In a copying apparatus of the type described, when it is desired to adjust the optical density of the copy, the dial on the exposure controller is turned to change the amount of light emitted by the exposure lamp. However, the direction of such adjustment is reversely related depending on whether the original is a negative or a positive image. Specifically, for a negative original, the amount of light from the lamp is increased in order to obtain an increased optical density while the light quantity is decreased for a reduced density. The reverse is true with a positive original. Thus, in the case of a positive original, the light quantity must be increased to provide a reduced optical density while an increased optical density is achieved with a reduced light quantity. As a result, the dial on the exposure controller must be turned in the opposite direction for a positive image from the direction in which it is turned for a negative image. This is inconvenient in practical operations, and often causes malfunctioning.